2020 R2 Geometric Tolerance migration help thread.

One error I have been getting with some of our older programs is datums that are not nominally perfectly perpendicular. The most common one is the rotate. I have been having to create offset points for Datum B to make it perpendicular. Also, it does not like 3d lines for rotate datums.

Introduction


The geometric tolerance command has detailed rules for feature types with surface data, for features types without surface data, and for features types that you cannot use in a geometric tolerance command at all. Unfortunately, some feature types are only allowed to be used with a few tolerance types, and that information is not detailed here. Also, there are a few exceptions to the rules detailed here that were omitted for clarity but are rare enough that we did not document them.

There are several types of features that you can use with the geometric tolerance command:

• Plane
  
• Cross section of a plane (surface line)
  
• Sample of a plane (surface point)
  
• Cylinder
  
• Cross section of a cylinder (surface circle)
  
• Surfaceless axis
  
• Width
  
• Cone
  
• Sphere
  
• Surfaceless 3D point
  
• Freeform
  

The documentation below talks about each PC-DMIS feature type and illustrates the kinds of PC-DMIS features that belong to the geometric tolerance command types.

Planes


With Surface Data

Plane feature types with surface data include:

Measured planes, auto planes (any measurement strategy), constructed BF planes, and constructed BFRE planes

No Surface Data

Plane feature types without surface data include:

Alignment planes, cast planes, mid-planes, perpendicular planes, parallel planes, primary datum planes, offset planes, translated planes, and generic planes

Only Allowed for Datums

Some plane types you can use only as datums, but not as considered features. These features include:

Alignment planes, cast planes, perpendicular planes, parallel planes, primary datum planes, offset planes, translated planes, and generic planes


Lines


With Surface Data

The geometric command always treats a line feature on a surface as a cross section of a planar surface. While you can measure a line on a non-planar surface in PC-DMIS, the geometric tolerance command always handles lines on surfaces as coming from a planar surface. These line types have surface data. They include these features:

Measured lines, auto lines (any measurement strategy), constructed 2D BF lines, constructed BFRE lines, and scan segment lines

Constructed 3D BFRE lines frequently have incorrect nominal values, even when you program your routine from a CAD model. Specifically, the nominal workplane of the constructed 3D BFRE line contains both the nominal surface normal and the nominal line vector. It is often nominally misaligned with the drawing. If you use this as a datum, it can frequently cause the following error message:

"Datum feature <feature name> is 2D. It needs a higher-precedence datum to constrain its workplane."

In most cases, we recommend using constructed 2D BFRE lines instead of constructed 3D BFRE lines so the nominal workplane of the line is correct.

No Surface Data

Some line features are cross sections of a plane, but they do not have surface data. These include:

Mid-lines, projected lines, and secondary datum lines

Some line features are surfaceless axes. These represent some axis of revolution and do not have a surface. These do not have surface data. These line features include:

Alignment lines, constructed 3D BF lines, cast lines, intersection lines, parallel lines, perpendicular lines, offset lines, and generic lines


Points


With Surface Data

A point feature on a surface is always treated as a sample of a planar surface. While you can measure a point on a non-planar surface in PC-DMIS, the geometric tolerance command always handles points on surfaces as coming from a planar surface. These point types have surface data. These point features include:

Measured points, vector points (default strategy, not the self-centering one), surface points, edge points, high points, mid-points, and tertiary datum points

No Surface Data

Some point features do not have a surface and are constrained in 3 dimensions just like the center-point of a sphere. These are surfaceless 3D points. These point features include:

Projection points and generic points

A pierce point is constrained in two dimensions, so it is a surfaceless axis having a length of zero. For information on surfaceless axes, see the " Lines" above.

Not Allowed

Several point features are not allowed as inputs to the geometric tolerance command, neither as considered features nor datums. These include:

Corner points, auto angle points, intersection points, origin points, drop points, cast points, vector distance points, and offset points.


Cylinders


With Surface Data

Cylinder feature types with surface data include:

Measured cylinders, auto cylinders (any measurement strategy), constructed BF cylinders, and constructed BFRE cylinders

No Surface Data

Cylinder feature types without surface data include:

Cylinders and generic cylinders

Not Allowed

Projection cylinders are not allowed as inputs to the geometric tolerance command, neither as considered features nor datums.


Circles


With Surface Data

Circle features are treated as a cross section of a cylindrical surface. While you can measure a circle on a non-cylindrical surface in PC-DMIS, the geometric tolerance command always handles circles as coming from a cylindrical surface (with one exception detailed in " Circular Runout").

Circle feature types with surface data include:

Measured circles, auto circles (except the gage scan calibration measurement strategy), constructed BF circles, constructed BFRE circles, and scan segment circles

Without Surface Data

Circle feature types that do not have surface data include:

Intersection circles, cast circles, tangent 2 lines circles, tangent 3 lines circles, tangent 3 circles, scan minimum circles, and generic circles

Not Allowed

Some circle feature types are not allowed as inputs to the geometric tolerance command, neither as considered features nor datums. These include:

Auto circles with the gage scan calibration measurement strategy, projection circles, cone circles, sphere circles, and cylinder circles


Widths


All width features have surface data.


Slots and Notches


With Surface Data

Slots and notches have surface data when you use them in a profile of a line tolerance.

No Surface Data

Slots and notches do not have surface data when you use them in a position tolerance or as a datum.

Be careful with slot and notch features.

You should only use them if you already know that the form of the features is very good. If you suspect that the manufactured form error might be significant, do not use a slot or notch command. Instead, measure a scan around the perimeter of the feature and then tolerance the form, orientation, and location of the feature with a profile of a line tolerance.


Cones


With Surface Data

Cone features with surface data include:

Measured cones, auto cones (any measurement strategy), constructed BF cones, and constructed BFRE cones

No Surface Data

Cast cones represent a conical surface but do not have surface data.

Generic cones don't have a diameter in PC-DMIS, and so they represent a surfaceless axis and do not have surface data.

Not Allowed

Projection cones are not allowed as inputs to the geometric tolerance command, neither as considered features nor as datums.


Spheres


With Surface Data

Sphere features with surface data include:

Measured spheres, auto spheres, constructed BF spheres, and constructed BFRE spheres

Without Surface Data

Sphere features without surface data include:

Cast spheres and generic spheres

Not Allowed

Projection spheres are not allowed as inputs to the geometric tolerance command, neither as considered features nor as datums.

Freeform Feature Types


The geometric tolerance command allows Freeform features as considered features for profile tolerances. These features have a number of measured points with matching nominal points and nominal vectors.

When there is no CAD model present, or when you don't use the iterate and re-pierce option, PC-DMIS calculates the deviations simply as the vector deviation of the measured point to the nominal planar surface defined by the nominal point and the nominal vector. This is the "piecewise planar" approximation.

When your measurement routine uses a CAD model, and you use iterate and re-pierce, PC-DMIS calculates the deviations to the CAD model (there is no piecewise planar approximation). For more information, see " Profile of a Line" and " Profile of a Surface".

PC-DMIS considers these feature types as considered freeform features:

Scan commands, constructed sets, constructed filtered sets, and constructed adjust filter objects, auto Profile2D features (vision), and torii

Possible Surface Data

PC-DMIS considers several feature types as freeform features (with surface data) when you use them in a profile tolerance, but it considers them as circle features (lacking surface data) when you use them in a position tolerance. These feature types aren't really designed for position tolerances, but they are included as circles (lacking surface data) for migration purposes. These feature types include:

Polygons, notches, slots, and ellipses

Not Allowed

These features or types of features are not allowed as inputs to the geometric tolerance command, neither as considered feature nor as datums:

Measured sets, area scans, projected ellipses, projected notches, projected slots, auto blobs, flush and gap features, load fixture features, face features, object features, constructed curve features, constructed surface features, mesh features, and gage features


Reverse Features


Several types of features are "reverse" features. These include:

Reverse planes, reverse cylinders, and so on

Possible Surface Data

Reverse features might have surface data. It depends on the input to the reverse feature. If the input has surface data, so does the reverse feature.

Possibly Allowed

You might be able to use reverse features as a considered feature or datum feature. It depends on the input to the reverse feature. The surface handling of the reverse feature is the same as the input feature. For example, a reverse line may be a surfaceless axis or a plane cross section. It depends on the input to the reverse feature.

Not Allowed

You cannot use reverse features that are constructed out of a different type of feature than the reverse feature as inputs to the geometric tolerance command, neither as considered features nor as datums. For example, you cannot use a reverse line constructed from a cylinder as an input to the geometric tolerance command.

It seems that you are viewing datum features almost as alignment elements. That is how XactMeasure behaved. What is the particular datum structure that you are struggling with? Does your 3D line constrain any available degrees of freedom?

JacobCheverie It's not an issue for me anymore cause I know what to do to fix it. It's just a reoccurring error I get when opening our older programs in R2 for the first time. Xact measure let users get away with more than they should have I believe.

So if I have a primary datum being a cylinder, and the secondary datum also being the cylinder, when i take edge points and define them as a set why does it still give the the error under line profile stating I need a work plane defined? The DRF shows a material boundary on both datums is it because when you apply a boundary to the secondary datum at that point its not fully constrained?

How would you go about defining that work plane of the linear open scan I am using so I can dimension it to the drawing.

So your primary and secondary datum features are both cylinders, and your datum references are both at MMB?

You are using edge points to measure cylinders? I would think that the edge points would construct a circle which is a 2D feature and thus does not define a workplane.

Your correct almost, I'll explain better I am using auto cylinder to dimension my cylinders, i am using edge points on the trim line to construct a feature set and I am trying to dimension the line profile of that feature set but it wont let me when i use the material boundary applied to both datums if i apply it to only of of the datums then it lets me dimension the line profile, if i try applying it to both then it states i need to define the workplane.

I think you have the right idea about why it doesn't work. Once you reference both datum features at MMB, there are no fully constrained DOF and thus no unique workplane from which conformance can be assessed.

Consider the case of only one datum. If you have a cylindrical primary datum feature referenced at RMB, you have a workplane established. To gage this part, you would use an expanding pin to contact the datum feature. The plane perpendicular to the axis of the pin would become your workplane. Now, assume you reference the datum feature at MMB. To gage this part, you would use a fixed size pin and the part can shift (two translations, two rotations) about the axis of the pin. The feature under the profile control has no single plane that the surface can be projected onto and compared to a tolerance zone because the workplane will depend on the amount of datum feature displacement.

The same analogy can work for two cylindrical datum features.

One solution is to reference one datum feature at RMB, because it is said that if it passes at RMB it will pass MMB. This may depend on how advantageous the MMB reference is to you. Also, you will need to assess whether [A(M)|B] or [A|B(M)] closer matches the function of [A(M)|B(M)] (I would assume the second option).

I agree totally, just wanted to ask the question before I told them their print is incorrect, I appreciate the support.